Summary - Evaluation and visualization of refrigerant two-phase flow in distributor

CHAPTER 6 CONCLUSION

6.1 Summary

This study investigated several possible factors influencing the performance of refrigerant distributor such as mass flow rate, distributor inlet quality and orientation in an air conditioning system using R134a as working fluid. Although the experiment facility is quite close to a real AC system, it is inevitable to have some deviation for the purpose of measurement. Effects of these differences from real system were analyzed. In addition, two-phase flow in distributor as well as the inlet tube was visualized by high-speed camera to understand the flow behavior. The main conclusions are as follows:

• Distribution of mass flow rate and quality show a similar pattern under different working conditions, in other words, some circuits always get more refrigerant than others.

• The performance of distributor is improved as mass flow rate increases because high velocity can result in more homogeneous flow.

• Lower distributor inlet quality also improves distribution. A possible explanation is that flow is closer to single phase as the percent of vapor phase decreased.

• Orientation has no effect on distribution, which indicates that two-phase flow does not separate in distributor.

• The existence of Micro Motion at downstream of evaporator improves the distribution to some degree. That is to say the performance of this distributor will be a little worse in a real system than estimated in this study.

• When different heat loads were provided to achieve the same superheat at the evaporator exits, the cooling capacity is larger than the situation with uniform heat load. Because for the first case, all the liquid phase refrigerant was fully utilized. However, the distribution of mass flow rate and quality have a similar pattern for these two cases.

• Visualization results show that it is annular flow at the inlet of distributor when refrigerant mass flow rate is extremely low. As the mass flow rate increases gradually, the flow is approaching to a more homogeneous state, and the distribution was improved accordingly.

6.2 Future work

This study mainly focused on the performance of refrigerant distributor. However, according to the visualization results, flow regime between expansion valve and distributor plays an important role in two-phase distribution. Bowers [32] has studied flow development after expansion device in a system without oil and briefly mentioned the effect of oil on flow regime. It seems that the existence of oil will change the flow regime and flow development dramatically. So, the future work will look into the effect of flow regimes in straight tube including L and U bends on flow development characteristics in adiabatic two-phase flow after an expansion device to help improving distribution, design of distributors, and inlet headers in the case of parallel flow evaporators. The effect of oil on flow regime and distribution will be taken into account, as is the case with real system.

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APPENDIX A PRESSURE DROP IN FEEDER TUBE

Figure 38 Adiabatic two-phase flow pressure drop as a function of mass flow rate and quality (horizontal, m=20 g/s, x=0.22)

Figure 39 Adiabatic two-phase flow pressure drop as a function of mass flow rate and quality (horizontal, m=25 g/s, x=0.22)

APPENDIX B CALCULATED PRESSURE DROP VS. MEASURED PRESSURE DROP

Figure 40 Comparison of pressure drop between calculated and measured values

APPENDIX C REPRESENTATIVENESS OF THE TRANSPARENT DISTRIBUTOR

Figure 41 Distribution of non-dimensional het load: original distributor vs. transparent distributor (vertical downward, x=0.22)

Figure 42 Distribution of non-dimensional het load: original distributor vs. transparent distributor (vertical upward, x=0.22)

APPENDIX D ORIGINAL DATA

Table 5 Experiment results under five working conditions at vertical upward orientation Working

conditions

Pressure [kPa]

Pxri Pdri Pero1 Pero2 Pero3 Pero4 Pero

1 1442.985 516.1281 439.2056 439.0234 433.8776 447.447 385.3771 2 1465.968 601.4576 501.7117 486.2614 478.8385 493.5885 375.0443 3 1461.834 692.1789 560.7321 535.0084 537.381 552.8681 375.0896 4 1455.81 644.2211 552.0674 525.3367 552.4155 549.3449 380.5918 5 1460.941 615.1711 550.526 530.7641 550.9162 550.2442 384.1812

Working conditions

Temperature [°C]

Txri Tero1 Tero2 Tero3 Tero4 Tref

1 44.76235 19.75431 20.33339 20.23777 21.22096 29.58302

2 47.48902 26.4123 25.83284 24.35898 26.74783 30.77232

3 49.26625 28.21003 27.46222 28.29933 28.31583 32.98008 4 39.21478 25.42353 24.80837 25.88787 24.69178 29.31158 5 31.12477 28.46387 26.75602 26.55728 27.42813 30.2052

Working conditions

Mass flow rate [g/s]

m1 m2 m3 m4 m

1 3.45566 3.707961 3.171342 3.89291 14.61754

2 5.042673 4.902464 4.335572 4.998566 19.45302

3 6.455076 6.192708 5.812087 6.416939 24.94322

4 6.014032 5.56024 5.904053 6.060355 24.55195

3 0.207454 0.272014 0.202759 0.221718 0.248565

4 0.147122 0.171586 0.092708 0.1321 0.159608

Table 6 Experiment results under five working conditions at vertical downward orientation Working

conditions

Pressure [kPa]

Pxri Pdri Pero1 Pero2 Pero3 Pero4 Pero

1 1446.902 515.5022 456.9994 440.2699 448.4777 449.1073 386.1563 2 1461.249 590.9212 497.3551 478.8713 492.3114 499.0313 387.556 3 1458.238 670.9173 549.5541 535.8722 540.6493 557.7974 386.7168 4 1463.867 645.3476 557.2861 552.6879 559.1974 558.2472 392.1295 5 1462.014 627.2165 567.7705 561.9906 568.181 564.3965 394.9225

Working conditions

Temperature [°C]

Txri Tero1 Tero2 Tero3 Tero4 Tero Tref

1 43.2995 17.26876 18.57784 17.3452 19.20776 25.85185 32.14038 2 46.2273 21.55124 20.73401 21.2348 20.76913 28.80309 33.69051 3 47.79116 25.27747 23.42194 23.82163 24.23428 30.42059 34.57808 4 38.7308 24.62983 24.45644 23.75809 24.57516 30.76251 34.17244 5 31.98858 24.2123 23.11542 24.29856 23.55474 29.85609 32.89952

Working conditions

Mass flow rate [g/s]

m1 m2 m3 m4 m

1 3.96672 3.407783 3.615904 3.734066 15.26399

2 5.012374 4.567939 4.748031 5.088716 20.07288

3 6.150969 5.908939 5.830954 6.303847 24.9964

4 6.204635 6.158973 6.110693 6.213446 24.96716

5 6.346112 6.255835 6.195656 6.256611 25.03581

Working conditions

Quality [-]

xeri1 xeri2 xeri3 xeri4 xxro

1 0.176625 0.279698 0.191727 0.169478 0.235381

2 0.182059 0.273325 0.176821 0.131049 0.240919

3 0.189475 0.236329 0.188455 0.1212 0.2349

Table 7 Experiment results under five working conditions at horizontal orientation Working

conditions

Pressure [kPa]

Pxri Pdri Pero1 Pero2 Pero3 Pero4 Pero

1 1445.598 508.435 450.5561 435.5951 441.6546 449.4663 380.0511 2 1456.736 582.6512 494.0639 476.2229 483.4305 492.9105 381.5041 3 1456.104 672.3467 564.9645 542.2404 536.7864 548.3432 383.3707 4 1460.188 632.2394 548.5633 545.5815 550.793 542.8984 387.4074 5 1459.642 609.8249 551.9911 550.7294 552.8777 548.3778 386.848

Working conditions

Temperature [°C]

Txri Tero1 Tero2 Tero3 Tero4 Tero Tref

1 41.59245 21.2502 20.75569 21.0055 21.09628 20.99258 26.32505 2 45.07297 23.76783 22.86262 22.14034 24.83547 26.55641 28.39277 3 47.09829 25.42194 25.24313 24.2164 25.31235 28.32469 30.08018 4 36.41074 23.64625 22.81811 24.02513 24.25335 28.59101 32.26469 5 29.71916 23.5567 23.1379 24.41548 24.49449 28.28983 31.25029

Working conditions

Mass flow rate [g/s]

m1 m2 m3 m4 m

1 3.68228 3.273985 3.397397 3.766965 15.11043

2 4.853691 4.502372 4.513052 4.953976 19.98724

3 6.375651 5.942196 5.665258 6.079213 25.17014

4 6.141811 6.158861 6.086233 6.0544 24.79308

3 0.159343 0.203692 0.220442 0.179638 0.230588

4 0.112817 0.084653 0.079984 0.094022 0.137666

5 0.050916 0.031324 0.034301 0.037158 0.083793

Working

Table 8 Experiment results without Micro Motion under three working conditions at vertical downward orientation

1 568.1358 424.87104 589.45449 658.475

2 768.2987 613.56809 776.34612 882.3935

3 1020.7976 864.20205 957.77198 979.3454

Table 9 Experiment results with uniform heat load under three working conditions at vertical upward orientation

Table 10 Experiment results with uniform heat load under three working conditions at vertical downward orientation

1 42.60836 21.79148 42.6695 17.56058 13.86535 23.18835 28.57893 2 45.44206 20.22119 51.89106 16.84137 16.0066 30.37674 30.73758 3 47.03176 22.07323 40.502 35.22524 22.68143 30.74851 31.32194

Working

Table 11 Experiment results with uniform mass flow rate under three working conditions at vertical downward orientation

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